The present invention relates to an automatic clamping means for clamping dies to a press ram or a press bed. More particularly, the present invention relates to a clamping means having an improved retaining system that is self-tightening and self-compensating, and that normally retains a clamp in the clamped position by the mechanical interaction of various components or elements of the clamp. An externally applied force is required to release the clamp. The clamp is continuously self-tightening and self-compensating and remains clamped unless and until the external force is applied.
There are two basic types of clamps utilized for clamping a die; the first is the toggle type and the second is the fluid pressure type. Considering first the toggle type, this refers to either a manual or automatic type of clamp which is generally retained in the clamping position by a toggle that locks over top-dead center or pre-top-dead center. This type of clamp, has, typically, a narrow locking window. Thus, a problem with this type of clamp is the continual wear which begins to loosen the toggle. This wear causes a change in clamping pressure and performance and changes the clamping angle and efficiency of the clamp. Furthermore, this type of clamp suffers the problem that if the die is too thick, when the die is positioned on the press or press bed, the toggle might not reach the "locking" window.
To overcome these problems, the toggle type of clamp must be regularly adjusted or replaced. If close and frequent inspections are not made, the toggle, which can wear as previously described, may break thus releasing the tool or die from the press ram with the attendant problems.
The second type of clamp, as briefly mentioned above, is the type of clamp which is generally controlled by hydraulic or pneumatic pressure. This type of clamp is retained in position by continuous "fluid" pressure forcing the clamp into engagement. If the pressure drops, as for example by a broken line, the clamp will loosen or release dramatically creating the possibility of damage to the machinery and equipment. Therefore, the fluid pressure type of clamp requires additional safety devices or additional safety features.